1. Scope of Invention
This invention relates generally to booster fans for airflow duct systems, and more particularly to an in-line booster fan for such duct systems which is fully automatically controlled by air duct operating conditions.
2. Prior Art
When there is a need for boosting or increasing the air flow within a duct system such as that associated with the removal of heated and moistened air discharging or venting from a clothes dryer, an axial flow booster fan is generally added somewhere along the length of the duct system. Such booster fan installations are typically required where the outlet vent or discharge for the duct system is remotely located from the clothes dryer or other vented appliance or equipment which discharges air for removal.
However, the booster fan is only needed and therefore ideally should only operate during the time periods of clothes dryer operation. In many cases however, it is impractical to control the operation of the booster fan using the electrical power supply from the appliance because of the remoteness between the booster fan and the appliance. Further, it is generally impractical to control the operation of the booster fan with conventional manually operated electric switches, again due to the remoteness of the booster fan location.
It is well known to utilize pressure differential sensors between the inside and the outside of the duct system or axial flow booster fan. Such a pressure switch which measures static or total pressure and may be triggered by either a positive or a negative pressure differential to accomplish this booster fan operation control. Such increased duct system static pressure occurs when the appliance begins to operate, causing the static pressure buildup in the duct system. However, erratic and undesirable operation is likely to result.
If the pressure sensor is located in one section of the duct system, the pressure change as a result of the booster fan operation may cause the pressure switch to open, prematurely shutting off the booster fan. Thereafter, the pressure switch will again close, restarting the booster fan. This undesirable on-off cycling of the booster fan continues until the appliance itself shuts off.
If the pressure switch is located in another section of the duct system, the booster fan will amplify the pressure differential, causing the pressure switch to remain closed, even when the appliance shuts off and its airflow into the duct system is discontinued.
With great care, the pressure sensing arrangement may be located in conjunction with the pressure buildup of each individual booster fan so as to timely energize and shut off the operation of the booster fan generally coincident with the operation of the appliance requiring system ventilation. However, this is a time-consuming and tedious procedure, requiring a higher level of technical competence in the installation.
The present invention utilizes the pressure sensing features which is indicative of appliance operation, but couples this pressure signal input to energize the booster fan with a predetermined time delay for shutting the blower fan off, e.g. about five to twenty minutes. Thus, no matter what pressure signal is used by the control device of the present invention, the booster fan will remain operational for the predetermined time period after which it will be shut off by the timed delay relay. Subsequent booster fan reactivation will occur each time pressure buildup in the duct system in close proximity to the booster fan reoccurs.